The investigations proposed for this project are directed toward a functional analysis of conditional stimulus control over visual choice discriminations in young normal and developmentally delayed persons. Emphasis is placed upon understanding principles involved in bringing selection of choice stimuli under conditional control of spoken words. Previous research has demonstrated that delayed persons, relatively sophisticated linguistically, can be trained to select one stimilus choice (out of two available choices) in the presence of one spoken word and will subsequently respond away from the trained choice on intermittent presentations of an untrained spoken word. Pilot data for a study to automate these procedures suggests latency of responding may be a more sensitive measure of control by the spoken words than choice selection alone. Latency measures may be predictive of subsequent demonstrations of the conditional control by changes in choice selection. A major portion of the proposed research is directed toward determining the necessary and sufficient conditions for establishing control over choice responding. The investigators are particularly interested in the role of previous experience with the class of stimuli which is used to indicate which of the choice selections will lead to reinforcement. They will attempt to provide the experience necessary for establishing the control at a generalized level under laboratory conditions. In addition, the investigators will also examine the nature of control by visual standards in a visual match-to-sample task. They are particularly interested in the relationship of the visual standard and the incorrect choice stimulus as well as the correct choice stimulus. Preliminary data suggests the subject may learn that the incorrect stimulus does not go with a given standard which can be demonstrated by responding away from that stimulus choice whenever the trained standard is present. These basic laboratory studies are viewed as specifying principles which may be used to improve the technology in applied settings responsible for training the developmentally delayed person.